Pigeon Fever is also known as Dryland Distemper, Pigeon Breast or Colorado Strangles in horses. Pigeon Fever is endemic to the southwestern United States and has risen dramatically over the past ten years and now affects most areas of the country. The bacterium involved is called Corynebacterium pseudotuberculosis. Corynebacterium pseudotuberculosis is found in three common species of flies—the housefly, the stable fly and horn fly, which are believed to be the major vectors for the disease. Horn flies, especially, feed on the ventral midline of the horse, which is where many abscesses start. The vector for spreading the disease from horse to horse is a flying insect with a range of about a quarter of a mile. As a result, quarantine is a very inefficient way of trying to limit the spread of this disease.
The basis for the name stems from the behavior of the disease. Pigeon Fever tends to cause abscesses in the chest area of the horse. As the abscess develops the chest swells much like the prominent chest of a pigeon.
Pigeon fever is an equine disease that can cause external or internal abscesses and/or an infection or ulcerative lymphangitis in the limbs. Abscesses may form between the jaw bones and in males, in the sheath. It can also affect the mammary area in a mare. The disease starts with a firm diffuse swelling over the affected region. The hard swelling enlarges and then softens like a water balloon as the abscess comes to a head.
Veterinary treatment usually consists of hot packing the swelling until an abscess has formed and is ready to lance. Once the abscess is lanced the open wound is cleaned daily and the affected horse is put on antibiotics for an extended period of time. The problem with Pigeon fever is that it can cause multiple abscesses in a given horse. Frequently horses will have a recurrence once the antibiotics are stopped. In rare cases a horse may even get an internal abscess which can result in peritonitis when it breaks open. The risk in administering antibiotics at first signs of the disease is that internal abscesses may form. It is for this reason that most cases require waiting until the abscess has formed and been lanced before instituting antibiotic treatment.
There is no vaccination for Pigeon Fever. The disease follows a pattern of having one or two years when many horses in an area will get the disease. Then several years will follow without any cases being seen. Because it is spread by flies, on a given ranch if one horse becomes affected, it is likely that a small number of additional cases will be seen. As a result, horses are either susceptible to the disease, or they have immunity as a result of natural exposure earlier in life. Unfortunately, the immunity which a horse develops from contracting Pigeon Fever does not last a lifetime. Horses will sometimes develop the disease more than once in their lives.
A need exists for methods and medicaments for preventing Pigeon Fever or for reducing the incidence or lessening the severity of clinical symptoms associated with such disease, including those associated with Corynebacterium pseudotuberculosis bacteria.